Sintered powdered metal piston ring



States SINTERED .POWDERED METAL PISTON RING Robert F. Thomson, Grosse Pointe Woods, Mich assignortoGeneral Motors Corporation, Detroit, Mich, a corporation. of Delaware N0. Dr pl cat o D cem e 2. 1954 SerialNo. 478,433

sor tm ciao-182.5 I

inindustry. during..-recent years; Heretofore, however,

porous-metallpartshavenot been successfullyfused in piston ringsbecause of their relatively low wear resistance. A principalnobject of the present invention, therefore, is to provide; ahovelsintered and forged or sintered and cold pressedtzpowdered.metal piston ring having. goodantifriction .propertiesanda high degree of wear resistance dneto the presence ofaluminunroxide. particles. A further object of. this .invention .is toeliminate .the' necessity ofiexpensive chromium plating of piston rings without sacrificin'g-wearresistanceby providing a powdered ferrous base pistonring containing hard aluminum oxide particles. Still axfurther object of the invention is to provide a simple and inexpensive process for forming a sintered, forged and/or pressed'powderedmetal pist-onringhaving proper porosity.

The above and other. objects areattained in accordance with'xmyinvention by a sintered and worked-powdered metaltpiston ringhaving controlled porosity and'high wear resistance due to the presence of'dispersed particles of aluminum oxide.

Tests on-pistonrings formed inaccordance with my invention-indicatethat the wear resistance of these rings comparesfavorably with that of chromium plated'rings. Moreover, asintered'powdered metal piston ring of this type can be- .inexpensively manufactured to close dimensional tolerances because of the elimination of the expensive machining operations otherwise necessary. Since little or nomachining is necessary, there is little scrap or waste. v

Recently,- sintered powdered ferrous base piston rings have been provided with increased Wear resistance by the inclusion of either nickel-titanium or titanium alurninum particles in the powdered metal mix. These deyelopments are respectively disclosed in copending patent application S; N: 317,737, filed October 30, 1952, in the name of Alfred L. Boegehold, newabandoned,--and co-pendin'g patent application S. N. 444,402, filed Julyv 19, 1954, in the names of Robert F. Thomson and Eric W. Weinrnan. However, the-use of aluminum oxide particles in the mix, in accordance with the present invention, affords. certain advantages-over the use of nickel-titanium or titaniumalu'minum particles, The hard, crystalline aluminum oxide particles are preferable from an economic standpoint since Alunduln and corundum, for example, cost appreatent 2,855,659 ll i-atented Oct. 14, 1958 2 whichthey are added to a negligible extent as compared Withnickel-containing compounds and tend to remain in substantially the same form in which they are introduced. Maximum wear resistance normally cannot'be obtained if the particles alloy excessively with the base metal of the powdered mix.

Other objects and advantages of the present. invention will more fully appear from thefollowi'ng detailed description of-a preferred embodiment of my invention.

A piston ringis preferably formed-in accordance'with my invention from amixture of powdered iron containing finely pulverized aluminum oxide. Even a relatively minute amount of the aluminum oxide powder improves the Wear resistance of thepiston ring-to an appreciable extent, and the range of this constituent may vary front a small but effective amountto a quantity constituting approximately 20% by weight of the ring. However, in order to reduce costs and to provide-the piston ringwith the desired strength, particularly impact strength and shockresistance, the aluminum oxide content'normallyshould be maintained between .about 0.25% and 10%. When more than 10% powdered aluminum oxide is used in -a sintered powdered ferrous base piston ring, the tensile strength and ductility of the ring aresomewhat reduced. This reduction inphysical properties becomes quite pronounced when the aluminum oxide content is raised above.20%. The brittleness of such a piston ring is evidenced by chipping or cracking of wear test specimens when they are being ground. Optimum propertie's'are usually obtained when the ring-contains approximately 1.5 to 6%. ofthe crystalline aluminum oxide powder. y

Finely-divided graphite, preferably 80 mesh or finer, maybe mixedwith the-metal; powder and-improves the quality of: the piston: ring if his present in'arnounts not larger than about 4% by weigh t. 'An initial carborl con tent-of; about 0.3 %"to 4% is-satisfactory, but-to-prevent loss ofstrengtli and hardness of thepiston ring thefgra'p hit e content should not exceed 4% inmost instances. Alt ernatively, the-desired amount of carbon may be added, or theinitial carbon content adjusted, by subsequent heat treatment, such as carburizing, of'the piston ring It will be-understood, o-f course,-that a measurable amount of the carbon is usually lost during the sinter'in'g'operation, and that it is the residualcarbon which is important in deter} mining. the. strength of the piston ring. Inasmuch: as sintering may reduce the initial carbon content by approximately one-third, it is desirable to controlth e carbon ciably'less than other typical; nickel-titanium alloys or n mlumi owde s, Of. ou se, um nu x de a b' oss n co tain. ny, r a vely r ica te ia s. u h as nif r mania n n iins;. nQt Q r .-the highrtneltin uminum oxide particlesl alloy withthe powdered metal mixto additions and sinter-ingoperation so that the residuahc bon content inthe piston ring is between approximately 0.3% and: 3% by weight. Thus, my preferred retained carboncontent ofabout 0.6% to 1.5% normally requires the. presence of. between 1% and 2.3% carbon-before sintering.

In view-of the above considerations, I have found that a sintered powdered metal piston ring having optimum wear resistance properties in accordance with the present invention comprises approximately 1.5% to 6% by weight of crystalline A1 0 powder, 0.6% to 1.5 by weight of carbon, and the balancesnbstantially'allironL If e e r s me al ista ing 1 e s e m ns of 'a multiple pressing} operation, as hereinafter described a smallbut effective amount of zinc stearate not in excess of about 2.5% mayalso be beneficially included infthe powdered iron mix. The zinc stearateeliminates any necessity for coating the dies with a lubricant during the briquetting operationf In general, Ihave found thatbest resultsare obtained with. a mix having a zinestearatecontent between. approximately- 0 3 and: 2%. Other die lubrieantgsuch as stearic acid. in powder form, can also be used inIplace of the zinc stearate.

Among the alnr ninum oxides which may be usedzrare I .fusedAl tj such as Alundum, and the'impure Al Ogcon- 1 1 taini-ng minor amounts: of iron oxide and known as ,Turki 1 ish. emery. Corundum (a form: of natural A1 and g 1 tabular coru ndum (Cal'cin'edA-l QQ likewise caujbe suei cessfully employed in accordance; with the; presentinvem i tion. Specific examplesof these formsof crystalline a1u1- 1minum1 oxides include the commercially available com- 1 "pounds identifiedas 'Alundum11600X,Alundum 320B, 1

' 1 Jcorundumf 300, tabular'corunduni :i00+;200 and Turk- 1 is'h' emery 320. The numerals following the alumina: 1 classification in .each instance indicate the approximate particle sizeofthe alumina particles. Theproper use of i 1 1 1 j appropriate amounts of any of theseforms of aluminum f 1 oxides in the manner hereinafter described results in the 1 .productionof a sintered powdered metal part having sub- 11 I l00 to 600 mesh aluminum oxide powder may be 1 1 used, but +25 0 to --3'S0 mess particles are preferred: 1 1 T 1 .1 i 1 Crystalline aluminum oxide particles which are too 1 are somewhat prone to cause scoring. .1 1 a 1 1 1 1 1 1 I 1 fAmjong the ferrous base materials which may be slic 1 1 1 t 1 eessfully .used are commercial iron powdergsuchas those 1 1 coarse 1 1 made :by griuding' scale,- deoxidizingj,;and pulverizing.

' 1 A steel powder, which may be produced by atomizihg very f 1 hard; steel, grinding and redu'cing the carbon content of 1 thepowder, can also be: employed- Moreover, 7 both i electrolytic iron and Swedish sponge non: powders areE I .1-satisfactory base materials for wear resistant powdered 1 1 ispreferably between -50 and 300 meshf 1 1 I 1 1 iron piston r'in'gsi 1 The particle size of the. iron powder 1 maybe produced by various processes; Onehighly satis- 1 1 factory method involves 1briquetting the mixture ofipo'w E dated iron, pulverized aluminum oxide, and graphite powder, it is desired to iadd the latter, at an. appropriate pressure in 1a: ring-shaped die, E thereby forming 1 g 1 1 thc; briquette' into] the shape of a complete fring. j :A 1

briqtietti'rig pressure of about 30,000 puuuds per square 1 inch has proved to be highly satisfactory; but pressures:

between approximately 20,000 and 120,000 pounds per square inch may be used. Before briquetting, it is im portant that the powdered metal constituents be thoroughly mixed in order to provide the resultant piston ring with uniform properties and structure.

1 The green briquette is then sintered under suitable conditions of time, temperature and atmosphere. Sintering temperatures between approximately 1900F. and

2300 F. and sintering periods between one-half hour and one hour are highly satisfactory. These sintering times are not critical, however, and sintering periods as short as four minutes and as long as 90 minutes are satisfactory. Excellent results have been obtained by sintering the briquette at 2100 F. for one hour under a nonoxidizing furnace atmosphere, such as Drycolene gas .or a gaseous mixture of Neutraleue" and a small amount of natural gas. 1 1 The dry Drycolene gas normally is composed of approximately 20% carbon monoxide, 3% hydrogen and 77% nitrogen. The Neutralene atmosphere mentioned above is a closely related gaseous mixture which usually consists of approximately 1.5% carbon monoxide, 1.5% hydrogen and197% nitrogen. It has proved advantageous to mix about 100 parts of Neutralene with one part of natural gas. 1 Other furnace atmospheres can be used, of course, but Drycolene and Neutralene are readily available and each providesa highly effective protective atmosphere. Gases with high hydrogen and very low carbon monoxide contents generally are less desirable because they have a greater tendency to decarburize the briquette and are morecostly.

After sintering, the strength of the piston ring blank maybe appreciably increased by cold pressing or forging it in a contour-shaped annular die into the desired piston ring blank shape. The forging operation is preferably one of hot forging, and itis usually expedient to chically, therefore, 1 have foiindlit? advisable to control; 1

"Ls'tantiallyimproved wear: resistance. Approximately 1 g r v v I r forging so as;to form apiston ring having between: 2% I 1 1 i 1 forge the ,briquette before it has cooled after; the: sintcr- 1 1 1 1 1 1 ing step. If desirethof course, the sintered briquette or 1 1 piston ring blank may. be permitted to cool and 1 then 1 i 1 1 1 1 1 be reheated @to a temperature; appropriate for forging. f 1 1 1 1 1 1 1 Forging temperatures approaching those used for sinter- I r r 1 ing are generally suitable for use in the present inven- 1 tion.1 In order to obtain particular properti s, however, 1

it is permissible to cold forge orcold press the piston 1 1 2 1 ring blank,%but:genierally a hotforgingoperationisprefer- 1 1 1 able. The forging or hot coining increases 1 the tensile 1 1 1 1 1 1 strength of; the sintered b11ank,especially as the porosity approaches zero. i Inasmuch ,as a dense structure permits scoring under severe engine operating couditijons it i I 1 1 1 is. desirable to carefully control the forging so as to pro- 1 vide ;t hei piston ring with. proper porosity. More speiand; 13 'porosity,=therebyimproving resistance to score.

1 If the ring fblanlr' is: to be compressed; or sized rather I i 1 1 thanforged, a pressureof about 40,000to 150,000 pounds i I persquare inch appropriate. 1 1

I 1 An'oth'er method :of forming the: wear-:resistantipiston 1 1 1 1 1 ring which has been particularly satisfactory involves 1 irepeatedpressing Iandsintering. In this' multiple pressing 1 1 I i 1 1 and annealing treatment,:the metal powder is first briquet-1 1 i 1 1 H 1 ted at about 30,000 to 90,000 pounds per square inch 9 1ingan= annular die, I The. hriquette is next presintered .at' 1 1 1 1 a temperature betweenapproxiinately .1 '600"F.1and 2100? i 1 i 1 1 i i-for; aboutlO minutesto two hours- A: presintering 1 period of one hour ;at ;a temperature of 1600? ;F; to I i 1 1 1 1650? F. produces i excellent: results: i iTh 11p 1sintered1 1 1 Q I 1 1 1 pistonring blank isthen sized or: pressed at room tem- 1 1 i 1 1 peratureat a pressure of. about 40,000to 150,000 pounds l i 1 1 1 1 1 per square {inch in the gsamezannular die/land; again sine Q 1 1 1 tered for about; 15 minutes to two hours at. a temper- 1 :ature between approximately 1 90091 F. and 2250" F. 1 1 1 1 1 'A1 one hour zsintering period 1at205 0i tof 1 2100 [F.- 1 1 1 1 1 1 1 is usually preferred. v'Tlmen the ring blank is again sized 1 fiat roorrr temperature at a 1 pressure of about; 40,000 to: 150,000 pounds per square inch'in a die' which is shaped to the contour of the ring in its free and open position, the blank still being in the shape of a complete ring,

however. 1 1 1 1 Following the forging or pressing operation, whichever is employed, the piston ring blank is preferably heated for about 30 to minutes to a temperature between approximately 800 F. and 1100 F. with or without restraining the shape of the ring blank. This operation reduces stresses from cold pressing and tempers the martensite formed during rapid cooling of the forged blank. It also may be used to correct the shape of the ring blank if it has become distorted during hot working. Tempering for approximately 45 minutes at 900 F. has proved to be highly satisfactory. If hot forging has been used, it is desirable to rapidly die cool the blank before heat treatment.

When the heat treatment has been completed, a small segment of the piston ring blank is removed by a machin- 1 ing operation to produce the necessary gap in the ring in its free position. After machining, the piston ring may be advantageously surfacetreated with a phosphate type of anti-friction material, such as iron-manganesephosphate. Other appropriate surface treatments could be used, of course.

It will be understood that a sintered powdered metal piston ring containing dispersed particles of aluminum oxide in accordance with this invention may be manufactured under the usual porous metal techniques .as dis- ,closed in a number of patents, such as Patents Nos. 1,738,163, 2,097,671, 2,075,444, etc. It is likewise obvious that other powdered iron alloys, as well as powdered steel and iron, can be used as the principal constituent in the piston ring. Also, instead of briquetting the metal powder as hereinbefore explained, it may be molded to shape as suggested in Koehring Patent No. 2,198,702 in which event the forgingoperatiom-asebefore, is used to provide the sintered powdered 'metalpiston ring; with optimum porosity.- All of'these modifications are to be considered as within seope o'f 'the present'g'invention, which broadly -comprehendstheprovisioinoFasintered powdered ferrous base-metalFpiston ringco'ntaining dispersed particles of "aluminum oxide:

Wear tests. were conducted to-compare sinteredpowde'red piston ring. materials formed in accordance 'with my invention with."conventional castiron 'piston rin'gmaterials. Eachsample'tofb'e tested wasmachinedto prepare a Miinchby, 1% inch rubbing surface. Thespecimens were next successively locked in a fixture 'oflthe wear test machine and placed in contact with a rotating smooth-surfaced cast iron wheel having a face width of one inch. Increased wear resistance was measured by decreased weight loss in grams and in decreased volume loss in cubic inches. Score resistance, on the other hand, was indicated by the load required to cause scoring under prescribed test conditions. The severity of this test is indicated by the fact that an amount of equivalent wear to that undergone in approximately 10,000 miles of engine operation occurs in an 18 /2 hour test run period.

A wear test using this apparatus was conducted in which the specimen load was increased during the 18 /2 hour period from zero load and automatically adjusted to produce a constant frictional load of 64 pounds. At the end of this test period the cast iron specimens showed an average weight loss of approximately 0.016 gram, while sintered powdered metal specimens containing crystalline A1 particles lost an average of only approximately 0.0045 gram. Similarly, while the conventional cast iron samples underwent a volume loss averaging about 140 l0 cubic inches, the specimens formed in accordance with the present invention changed on the average only 22 10* cubic inches. The results of this test, showing the low weight and low volume loss of my new piston ring under severe wear tests, illustrate its high wear resistance.

Likewise, tests indicate that my new and improved wear-resistant piston ring material has considerably better anti-friction properties than cast iron. This property was measured by means of the specimen load required to produce a 64 pound frictional load. Thus, samples formed of sintered powdered iron containing the aforementioned dispersed particles of crystalline A1 0 required an average of about 830 pounds specimen load to produce the 64 pound frictional load as compared with an average of only approximately 650 pounds specimen load when the cast iron samples were tested.

The importance of the aluminum oxide particles in my new sintered and worked piston ring material is apparent when the results of the above tests are compared with tests conducted on the same sintered and forged powdered iron material to which aluminum oxide had not been added. For example, the specimen load required to produce a 64 pound frictional load on the latter samples averaged only approximately 568 pounds, thus indicating that the coefficient of friction of such a material is substantially reduced by the presence of the crystalline A1 0 particles. Likewise, under the aforementioned test conditions, the ordinary sintered and forged powdered iron piston ring material lost an average of 0.028 gram and underwent a reduction in volume averaging about 238 10- cubic inches.

When these piston ring materials were also subjected to a score test and compared, the specimens formed from the conventional powdered iron mix required a load averaging only 590 pounds to produce scoring, but an average load of approximately 697 pounds was required to cause any indication of scoring of my new sintered powdered metal piston ring material.

While the present invention has been described by means of certain specific examples, it is to be understood that other forms may be adopted and are contemplated as vbeingyvithin the scope of the! present invention as. set

fdftlfiii the. f6ll6wingclaims.

1. A porous piston ring for an internal'combustion engine, said piston .ring being characterized byhigh wear resistance and being formedof a sintered'and worked powdered metal comprising; approximately 0.3% to 3.%-carbon, 1.5% to 6% of crystalline A1 Q and.the balanceisubstantially all iron.

2. In. an internal" combustion engine, a highly. wearresistant piston ring formed are sintered andiwor ked powdered metal "consisting essentially of approximately 0.31%tb 37%? by weight 'of'carbon,,0.25% to- -l0'% "by weighbof' dispersed, hard particles of aluminum oxide, and the balance substantially all powdered iron.

3. The process of forming a powdered iron piston ring characterized by high wear resistance, said process comprising compressing a powdered metal mixture into an annular briquette, said mixture comprising approximately 0.3% to 4% graphite, 1.5 to 6% aluminum oxide which has been pulverized to form particles of -l00 to 600 mesh size, and the balance substantially all iron; subsequently sintering said briquette; thereafter sizing the annular briquette at a pressure of about 40,000 to 150,- 000 pounds per square inch in a die which is shaped to the contour of the ring in its free and open position; and thereafter working said sintered briquette to provide it with optimum strength and porosity.

4. A process of forming a porous piston ring which comprises mixing pulverized A1 0 with iron powder, briquetting the resultant mix at a pressure between 20,000 pounds per square inch and 120,000 pounds per square inch into an annular form, sintering the formed briquette under a nonoxidizing atmosphere for a period of time ranging from four minutes to minutes at a temperature between approximately 1900" F. to 2300 F., subsequently forging said sintered briquette to a porosity between 2% and 13% in a die which is shaped to the contour of the finished ring in its free and open position, die cooling the formed piston ring blank, and thereafter tempering said blank for approximately 30 to 60 minutes at a temperature between 800 F. and 1100 F.

5. A process of forming a powdered metal piston ring characterized by high wear resistance, said process comprising forming a powdered iron mixture containing approximately 0.25% to 10% by weight of hard particles of finely pulverized A1 0 briquetting said mixture at a pressure of about 30,000 to 90,000 pounds per square inch in an annular die, sintering said briquette at a temperature between approximately 1900 F. and 2250 F. for about 15 minutes to two hours, thereafter sizingthe formed piston ring blank at room temperature at a pressure of about 40,000 to 150,000 pounds per square inch in a die which is shaped to the contour of the ring in its free and open position, and subsequently tempering said blank for approximately 30 to 60 minutes at a temperature between 800 F. and 1100 F.

6. A process for forming a powdered metal piston ring characterized by high wear resistance, said process comprising forming a mixture consisting of 1.5% to 6% by weight of finely divided crystalline aluminum oxide, 0.3% to 4% by weight of graphite and the balance substantially all powdered iron, briquetting said mixture at a pressure of about 30,000 to 90,000 pounds per square inch in an annular die, presintering said briquette at a temperature between approximately 1600 F. and 2100 F. for about 10 minutes to two hours, thereafter sizing the formed piston ring blank at room temperature at a pressure of about 40,000 to 150,000 pounds per square inch in an annular die, again sintering said blank for approximately 15 minutes to two hours at a temperature between approximately 1900 F. and 2250 F., thereafter again sizing said blank at room temperature at a pressure of about 40,000 to 150,000 pounds per square inch in a die which is shaped to the contour of the ring 111115 free and open positi'omand subsequently tempering j FOREIGN PATENTS said blank for approximately"30'to 60 minutesat a'tem- 750 Germahy 'i 1.944 p r between and I T E' 274,017 "switzerlai June 1, 1951 896360 Ger any Nov. 12, 1953 References Cited in thefile of this patent I 5 896,36} Germany Nov. 12, 1953 UNITED STATES PATENTS T 3 T OTHER REFERENCES 2,072,070 Fisher Feb.'23, 1937 Alloy Cast Irons Handboo publ. by American 2,213,523 Jones et a1. Sept, 23 1940 v Fqundrymans Assn., 1944, pp. 252, 253. l 2,224,595 Dawihl Dec. 10, 1940 10 Goetze1: Treatise on Powder Metallurgy, New York 2,337,588 Calkins Dec. 28, 1943 Interscier we, 1949, 1950, vol. I, pp. 403, 698;vo1. II, 2,376,757 Chanosky May 22, 1945 p. 765. Also vol. I, pp. 680, 681,698; vol. II pp. 348- 2,404,598 Sachse July 23, 1946 352. 

1. A POROUS PISTON RING FOR AN INTERNAL COMBUSTION ENGINE, SAID PISTON RING BEING CHARACTERIZED BY HIGH WEAR RESISTANCE AND BEING FORMED OF A SINTERED AND WORKED POWDERED METAL MIX COMPRISING APPROXIMATELY 0.3% TO 3% CARBON, 1.5% TO 6% OF CRYSTALLINE AL2O3, AND THE BALANCE SUBSTANTIALLY ALL IRON. 